This invention is directed to fuel injector nozzles for partial oxidation gasifiers and more particularly to a novel fuel injector nozzle having a protective refractory insert at the outlet orifice to resist thermal and thermo-chemical damage to the fuel injector nozzle at the outlet orifice.
The processing of carbonaceous fuels, such as coal, gas, and oil to produce gaseous mixtures of hydrogen and carbon monoxide, such as coal gas, synthesis gas, reducing gas, or fuel gas, is generally carried out in a high-temperature environment of a partial oxidation gasifier, such as shown in U.S. Pat. No. 2,809,104. Partial oxidation gasifiers usually include annulus type fuel injector nozzles, as shown, for example, in U.S. Pat. No. 4,443,230 to Stellaccio (4 annulus fuel injector nozzle) and U.S. Pat. No. 4,491,456 to Schlinger (5 annulus fuel injector nozzle). The annulus type fuel injector nozzle is used to introduce pumpable slurries of carbonaceous fuels into a reaction chamber of the gasifier, along with oxygen-containing gases for partial oxidation.
In general, a water-coal slurry, which includes sulfur-containing materials, is fed into the reaction chamber of the gasifier through one or more annuli of the fuel injector nozzle. An oxygen-containing gas, flowing through other fuel injector annuli, meets with the water-coal slurry at an outlet orifice of the fuel injector nozzle and self-ignites at typical gasifier operating temperatures of approximately 2400 F. to 3000 F. Usual pressures within the gasifier environment can range from 1 to 300 atmospheres.
Within the gasifier environment, gaseous hydrogen sulfide, a well-known corrosive agent with respect to metal structure of the fuel injector nozzle, is generally formed during processing of the water-coal slurry component of the fuel feed. Liquid slag is also formed as a by-product of the reaction between the water-coal slurry and the oxygen-containing gas, and such slag also has a corrosive effect on the metal structure of the fuel injector nozzle. In addition, high temperature conditions at a reaction zone around the outlet orifice of the fuel injector nozzle due to self-ignition of the fuel feed components in this area can cause hot corrosion and thermal-induced fatigue cracking of the outlet orifice. The outlet orifice of the fuel injector nozzle generally defines the location of the highest thermal gradient zone in the gasifier.
Because of the corrosive effects of hydrogen sulfide and liquid slag on the fuel injector nozzle, especially at the outlet orifice, as well as the hot corrosion and thermal-induced fatigue cracking of the outlet orifice, failure or breakdown of the fuel injector nozzle is often likely to occur at the outlet orifice due to thermal damage and thermo-chemical degradation.
Such thermal damage and thermo-chemical degradation of the fuel injector nozzle structure limits the service life of the fuel injector nozzle, which must then be repaired or replaced. However, repair or replacement of a fuel injector nozzle is costly and inconvenient since the gasifier operation must be temporarily shut down for a cool-down period before the fuel injector can be removed for replacement or repair.
Attempts to limit fuel injector nozzle damage due to heat and corrosive agents include the provision of frusto-conical shields of thermal and wear-resistant material, such as tungsten and silicon carbide attached at the downstream end of a fuel injector nozzle, as shown in U.S. Pat. No. 4,491,456 to Schlinger. However, the frusto-conical shield shown by Schlinger is held in a vertical orientation and can easily slip away from the nozzle. Furthermore, any bonding materials for securing the Schlinger frusto-conical shield to the outlet end of the fuel injector nozzle may be subject to corrosion and bond failure. Failure of the bonding materials can cause the frusto-conical shield to fall away from the fuel injector nozzle. Thus, the protective service life of the Schlinger frusto-conical shield at the outlet end of the fuel injector nozzle may be prematurely reduced by a failure of the bonding agents that secure the frusto-conical shield to the fuel injector nozzle. The fuel injector nozzle is thus likely to have a reduced service life because of the premature loss of protective shielding provided by the frusto-conical shield.
Published Canadian Application 2,084,035 to Gehardus et. al. shows a burner for production of synthesis gas wherein the end surface is clad with ceramic platelets held in place by a dovetail joint. The dovetail joint creates a non-uniform thickness of the orifice wall at the dovetail joint and has a undesirable area of reduced wall thickness. The area of reduced wall thickness is a stress concentration area that is vulnerable to cracking and thermal damage. The non-uniform wall thickness at the dovetail joint can also lead to accelerated wear and corrosion. In addition the dovetail joint forms a narrow support neck for the ceramic platelets. The narrow support neck is an area of weakness and vulnerability of the platelets to damage or separation from the burner.
It is thus desirable to provide a fuel injector nozzle with a protective refractory insert that is securely retained at the outlet orifice of the fuel injector nozzle and which refractory insert replaces metal in the highest thermal gradient zone of the fuel injector nozzle. It is also desirable to provide a fuel injector nozzle with a protective refractory insert that remains in position under conditions which promote heat and hydrogen sulfide assisted thermal fatigue corrosion damage, whereby the enduring presence of the protective refractory insert extends the service life of the fuel injector nozzle.